1. Field of the Invention
The invention pertains to a composition useful in treating glass fibers or mineral fillers in order to bond them to polyolefins to form reinforced composites. In one embodiment, the composition is applied to glass fibers and mineral fillers embedded in a polyolefin. The application of this composition to fibers and fillers significantly improves fiber strand integrity and adhesion between fibers or fillers and the polyolefin in which the fibers and/or fillers are disposed.
2. Description of the Prior Art
Although the use of polyolefins is widespread, certain applications require levels of dimensional stability, tensile and flexural strength/modulus and impact resistance not obtainable with polyolefins as such. To meet these demands, reinforced polyolefins have been developed; the typical reinforcing agent being glass fibers. Much of the strength advantage offered by these composites, however, depends on how well the glass fiber adheres to the polyolefin. For example, when there is sufficient bonding between the polyolefin and the glass, shock energy will be transferred to the more robust glass reinforcing agent when the composite is impacted; on the other hand, if the bond is inadequate, the energy will be deleteriously distributed and the composite will fracture. Moreover, some composite fabrications require the use of an extruder, the aggressive conditions of which will break up a coated filament if the integrity of the glass-to-polymer bond is too low.
In consequence, various techniques have been explored to improve the adhesion between the glass fiber and the polyolefin. The more prevalent of these involves the use of sizing compositions, which treat the glass fiber to facilitate adhesion with the polyolefin. Because the typical polyolefin effectively has no chemical moieties that are reactive, efforts to tailor the sizing composition to ameliorate bonding to the polyolefin have been assayed.
For example, U.S. Pat. No. 4,240,944 describes a sizing composition comprised of an aqueous emulsion containing isotactic carboxylated polypropylene, base and surfactant; the sizing agent can further contain a film former which can be, among other things, polyurethane.
U.S. Pat. No. 4,728,573 relates a sizing composition having one or more amino organo coupling agents, an aqueous emulsion of an acid or anhydride modified polyolefin having one or more surfactants, wherein the polyolefin is neutralized with an organic or inorganic base with a basicity less than the basicity of the amino moiety of the coupling agent, a binder stabilizer, one or more film forming polymers and water.
While carboxylating the polyolefin component manifests in some improvement, the coated glass fibers that result often have poor strand integrity, as well as color problems. Furthermore, carboxylated compositions typically have poor emulsive properties in the first instance which hamper implementation of this strategy inasmuch as emulsions are the industrially preferred method of coating glass fibers.
Polyurethanes are well known for their adhesive properties in various use settings, including binding fibers together. Polyurethanes as such, however, do not adhere well to polyolefins such as polypropylene. To facilitate matters, attempts have been made to employ polyurethanes as such in concert with carboxylated polyolefins. Although such efforts have generally improved glass processing aspects of this technology, the cost has been a diminishment in composite properties. Efforts to modify polyurethanes for such end uses have also been explored; for example, U.S. Pat. No. 4,507,430 discloses a water based polyurethane emulsion constituted of a hydrogenated polyalkadiene polyol component useful as an adhesive or coating material for polyolefin. Nonetheless, the results merit further improvement. Accordingly the utilization of polyurethanes in treating glass fibers for reinforcement of polyolefin matrices has been limited.
Hence the art recognizes a continuing need to develop better techniques for adhering glass fibers and polyolefins to produce stronger and more durable reinforced composites.
A new sizing composition has now been developed which is particularly appropriate for use as a coating composition of glass fibers and the like which is employed as a polyolefin reinforcing agent. This sizing composition employs a new polyurethane dispersion that very well adheres to a hydrophobic matrix such as that provided by polyolefins.
In accordance with the present invention a sizing composition is provided. The sizing composition of the present invention includes a polyurethane dispersion which is a reaction product of a prepolymer and a chain extender. The prepolymer is a reaction product of a hydroxylated polymer selected from the group consisting of polyether polyols, polyester polyols and mixtures thereof, a hydroxylated polyalkadiene, a polyisocyanate, a compound having a pendent acid group, optionally, an ester of a fatty acid having about 12 to about 20 carbon atoms containing hydroxyl groups, a coupling agent and a polyolefin wax.
Alternatively, the prepolymer is a reaction product of a hydroxylated polymer selected from the group consisting of polyether polyols, polyester polyols and mixtures thereof, a hydroxylated polyalkadiene, a polyisocyanate, a bis(hydroxyalkyl)quaternary ammonium group-containing diol and, optionally, an ester of a fatty acid having about 12 to about 20 carbon atoms containing hydroxyl groups.
The sizing composition of the present invention includes a polyurethane dispersion, a coupling agent and a polyolefin wax. A first component of the sizing composition, a polyurethane dispersion, is a reaction product of a prepolymer and a chain extender. The prepolymer, in one preferred embodiment, is a reaction product of a hydroxylated polymer, a hydroxylated polyalkadiene, a polyisocyanate, a compound having a pendent acid group and, optionally, an ester of a hydroxylated fatty ester having between about 12 and about 20 carbon atoms. The chain extender is preferably an amine-containing compound.
The hydroxylated polymer in one preferred embodiment is a polyether polyol. Preferably, the polyether polyol is polyethylene glycol, polypropylene glycol or mixtures thereof.
In an alternate preferred embodiment the hydroxylated polymer is a polyester polyol. It is further preferred that the polyester polyol be poly(hexamethylene adipate/isophthalate) glycol or poly(hexamethylene orthophthalate) glycol.
A second component of the reaction product that produces the polyurethane dispersion prepolymer is a hydroxylated polyalkadiene. The hydroxylated polyalkadiene may or may not be hydrogenated. In those embodiments wherein the hydroxylated polyalkadiene is hydrogenated, any and all degrees of hydrogenation are within the contemplation of the present invention. In a particularly preferred embodiment, the hydroxylated polyalkadiene is a hydroxylated polybutadiene. Thus, a polybutadiene diol, whether or not partially or completely hydrogenated, is preferred.
A third component of the reaction product that forms the prepolymer is a polyisocyanate. Although any compound possessing at least two isocyanate groups is within the contemplation of the present invention, it is preferred that the polyisocyanate be a diisocyanate.
Both aliphatic and aromatic polyisocyanates may be utilized as a reactant in the formation of the prepolymer. However, aliphatic polyisocyanates are preferred. In view of these preferences it is apparent that aliphatic diisocyanates are particularly preferred. Thus, such aliphatic diisocyanates as isophorone diisocyanate (IPDI), hexamethylene diisocyanate, dicyclohexylmethane-4,4-diisocyanate and mixtures thereof are preferably employed in the formation of the prepolymer.
A fourth component of the reaction product which forms the prepolymer is a hydroxylated compound having a pendent acid group. The hydroxylated compound having a pendent acid group is preferably a hydroxylated compound having a pendent carboxylic acid group or hydroxylated compound having a pendent sulfonic acid group. Dimethylolpropionic acid (DMPA) and bis-hydroxyethyl aminoethane sulfonic acid (BES) are particularly preferred examples of the respective two preferred classes of compounds within the scope of the present invention.
An optional fifth component of the prepolymer is an ester of a fatty acid having from about 12 to about 20 carbon atoms containing hydroxyl groups. More preferably, the optional component is an ester of a fatty acid having about 15 to about 20 carbon atoms containing hydroxyl groups. Most preferably, the optional component is an ester of a fatty acid having about 18 carbon atoms containing hydroxyl groups. Thus, a particularly preferred embodiment of an ester of a fatty acid containing hydroxyl groups is glycerol monostearate.
In a second preferred embodiment the prepolymer reaction product is identical to the reaction product of the first preferred embodiment but for the substitution of a bis(hydroxyalkyl) quaternary group-containing diol for the hydroxylated compound having a pendent acid group in the first embodiment.
In this second preferred embodiment wherein a bis(hydroxyalkyl) quaternary grop-containing diol is present in the prepolymer reaction product, it is particularly preferred that the diol be bis(hydroxylated) quaternary ammonium methane sulfonate.
The prepolymer is reacted with a chain extender to form the polyurethane dispersion component of the coating composition of the present invention. The chain extender is preferably an amine compound. Of the amine-containing compounds within the scope of the chain extender of the present invention, hydrazine, isophorone diamine, aminoethylaminoethanol and polyalkylene diamines, such as hexamethylene diamine, are particularly preferred.
A second component of the sizing composition of the present invention is a coupling agent. As those skilled in the art are aware, coupling agents are organometallic compounds which improve adhesion between the fibrous reinforcement agent and the composite matrix. Among the coupling agents within the contemplation of the sizing composition of this invention, silanes are preferred. Specific silanes preferred for use in this application are aminosilanes and epoxysilanes. Other preferred coupling agents that may be used include methacrylate chromic chloride, titanium acetyl acetonate and the like.
A third component of the sizing composition is a polyolefin wax. Preferably, the polyolefin wax is a carboxylated polyolefin. More preferably, the carboxylated polyolefin is a carboxylated polyethylene, a carboxylated polypropylene or a mixture thereof.
To prepare the sizing composition the polyurethane dispersion is blended with an emulsion of the polyolefin wax in which the polyolefin wax, preferably a carboxylated polyolefin, is neutralized with a base. This blending operation is conducted under ambient temperature and pressure. The thus formed blend is diluted with water whereupon the coupling agent is added to the stirred blend.
In a preferred embodiment the aqueous sizing composition comprises between about 0.5% and about 4.0% polyurethane dispersion; between about 0.5% and about 4.0% polyolefin wax; between about 0.3% and about 0.6% coupling agent and the remainder water. The above percentages are by weight, based on the total weight of the aqueous sizing composition.
In a particularly preferred embodiment the sizing composition includes about 1.2% polyurethane dispersion, about 1.0% polyolefin wax and about 0.2% coupling agent, said percentages being by weight, based on solid content, the remainder being water.